The complete DNA sequence of human papovavirus BKV(Dun), consisting of 5153 nucleotide pairs, was obtained. The segments of the genome which correspond to the replication origin, the tandem repeated sequences, the 5' and 3' ends of the mRNAs, the splice sites, the early and late viral proteins and the putative viral polypeptides, have been identified and mapped. The BKV DNA sequence was also compared with analogous regions in the SV40 and polyoma virus genomes in an attempt to localize viral functions for lytic growth and transformation. A rapid technique was developed to sequence double stranded DNA fragments.